It is well known that the rotating blades of turbo-machinery such as gas turbine engines may be excited into undesirable modes and magnitudes of vibration by forces exerted on the blade during operation of the machine. Left unchecked, such vibration can cause a blade to fatigue prematurely or even to fail catastrophically.
U.S. Pat. No. 5,820,343 describes an airfoil vibration-damping device that attaches to the airfoil platform and extends into a cooling air passage along a radial length of the airfoil. The damping device includes a plurality of bearing surfaces that make contact with the walls of the cooling air passage to dampen vibration of the airfoil during operation of the turbine in which the airfoil is used.